implement 100% coverage for the core domain

backend/phpstan-baseline.neon

@@ -5,14 +5,33 @@ parameters:
 			identifier: argument.type
 			count: 1
 			path: public/index.php
-		-
-			message: '#^Method App\\Normalizer\\Normalizer\:\:toArray\(\) should return array\<string, mixed\> but returns array\|ArrayObject\|bool\|float\|int\|string\|null\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Normalizer/Normalizer.php
 
 		-
 			message: '#^Property App\\Entity\\User\:\:\$id \(int\|null\) is never assigned int so it can be removed from the property type\.$#'
 			identifier: property.unusedType
 			count: 1
 			path: src/Entity/User.php
+
+		-
+			message: '#^Cannot call method getLogging\(\) on App\\Instrumentation\\Instrumentation\|null\.$#'
+			identifier: method.nonObject
+			count: 1
+			path: src/Instrumentation/InstrumentationHolder.php
+
+		-
+			message: '#^Cannot call method getMetrics\(\) on App\\Instrumentation\\Instrumentation\|null\.$#'
+			identifier: method.nonObject
+			count: 1
+			path: src/Instrumentation/InstrumentationHolder.php
+
+		-
+			message: '#^Cannot call method getTracing\(\) on App\\Instrumentation\\Instrumentation\|null\.$#'
+			identifier: method.nonObject
+			count: 1
+			path: src/Instrumentation/InstrumentationHolder.php
+
+		-
+			message: '#^Method App\\Normalizer\\Normalizer\:\:toArray\(\) should return array\<string, mixed\> but returns array\|ArrayObject\|bool\|float\|int\|string\|null\.$#'
+			identifier: return.type
+			count: 1
+			path: src/Normalizer/Normalizer.php

backend/src/Instrumentation/InstrumentationHolder.php

@@ -4,6 +4,7 @@
 
 namespace App\Instrumentation;
 
+use App\Invariant\Ensure;
 use Psr\Log\LoggerInterface;
 
 final class InstrumentationHolder
@@ -12,7 +13,7 @@ final class InstrumentationHolder
 
     public static function initialize(string $telemetry, LoggerInterface $logger): void
     {
-        assert(in_array($telemetry, ['PsrLog', 'Null'], strict: true), 'Either "PsrLog" or "Null" is allowed for parameter $telemetry!');
+        Ensure::that(in_array($telemetry, ['PsrLog', 'Null'], strict: true), 'Either "PsrLog" or "Null" is allowed for parameter $telemetry!');
 
         if (is_null(self::$instance)) {
             self::$instance = new Instrumentation($telemetry, $logger);
@@ -21,21 +22,21 @@ public static function initialize(string $telemetry, LoggerInterface $logger): v
 
     public static function getLogging(): LoggingInterface
     {
-        assert(!is_null(self::$instance), 'Not yet initialized!');
+        Ensure::that(!is_null(self::$instance), 'Not yet initialized!');
 
         return self::$instance->getLogging();
     }
 
     public static function getMetrics(): MetricsInterface
     {
-        assert(!is_null(self::$instance), 'Not yet initialized!');
+        Ensure::that(!is_null(self::$instance), 'Not yet initialized!');
 
         return self::$instance->getMetrics();
     }
 
     public static function getTracing(): TracingInterface
     {
-        assert(!is_null(self::$instance), 'Not yet initialized!');
+        Ensure::that(!is_null(self::$instance), 'Not yet initialized!');
 
         return self::$instance->getTracing();
     }

backend/tests/Unit/Instrumentation/InstrumentationTest.php

@@ -8,6 +8,7 @@
 use App\Instrumentation\LoggingInterface;
 use App\Instrumentation\MetricsInterface;
 use App\Instrumentation\TracingInterface;
+use App\Invariant\InvariantException;
 use PHPUnit\Framework\TestCase;
 use Psr\Log\NullLogger;
 
@@ -79,15 +80,15 @@ public function test_provider_provides_tracing_interface(): void
 
     public function test_provider_throws_on_uninitialized_access_logging(): void
     {
-        $this->expectException(\AssertionError::class);
+        $this->expectException(InvariantException::class);
         $this->expectExceptionMessage('Not yet initialized!');
 
         InstrumentationHolder::getLogging();
     }
 
     public function test_provider_throws_on_invalid_telemetry_option(): void
     {
-        $this->expectException(\AssertionError::class);
+        $this->expectException(InvariantException::class);
         $this->expectExceptionMessage('Either "PsrLog" or "Null" is allowed');
 
         InstrumentationHolder::initialize('InvalidOption', new NullLogger());

backend/tests/Unit/SplitFairly/CompensationTest.php

@@ -48,6 +48,10 @@ public function test_compensation_when_first_user_spent_more(): void
         // User1 spent 50, so owes 25. User2 spent 25, so owes 12.5. Difference: 25 - 12.5 = 12.5
         self::assertSame(12.5, $compensation->settlement->value);
         self::assertSame('EUR', $compensation->settlement->currency);
+        self::assertSame(
+            sprintf('From: "%s" - to: "%s" - price: "%s"', $compensation->from, $compensation->to, (string) $compensation->settlement),
+            (string) $compensation
+        );
     }
 
     public function test_compensation_when_second_user_spent_more(): void

backend/tests/Unit/SplitFairly/EventTest.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\SplitFairly;
+
+use App\SplitFairly\Event;
+use PHPUnit\Framework\TestCase;
+
+final class EventTest extends TestCase
+{
+    public function test_constructor_sets_properties(): void
+    {
+        $createdBy = 'user-1';
+        $subjectType = 'Expense';
+        $subjectId = 'exp-1';
+        $eventType = 'tracked';
+        $payload = ['price' => 10.0, 'currency' => 'EUR'];
+        $createdAt = new \DateTimeImmutable('2026-02-12T07:00:00Z');
+
+        $event = new Event(
+            createdBy: $createdBy,
+            subjectType: $subjectType,
+            subjectId: $subjectId,
+            eventType: $eventType,
+            payload: $payload,
+            createdAt: $createdAt
+        );
+
+        self::assertSame($createdBy, $event->createdBy);
+        self::assertSame($subjectType, $event->subjectType);
+        self::assertSame($subjectId, $event->subjectId);
+        self::assertSame($eventType, $event->eventType);
+        self::assertSame($payload, $event->payload);
+        self::assertSame($createdAt, $event->createdAt);
+    }
+
+    public function test_get_value_returns_payload_value(): void
+    {
+        $event = new Event(
+            createdBy: 'user-1',
+            subjectType: 'Expense',
+            subjectId: 'exp-1',
+            eventType: 'tracked',
+            payload: ['price' => 10.0, 'currency' => 'EUR'],
+        );
+
+        self::assertSame(10.0, $event->getValue('price'));
+        self::assertSame('EUR', $event->getValue('currency'));
+    }
+}

backend/tests/Unit/SplitFairly/QueryOptionsTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\SplitFairly;
+
+use App\SplitFairly\QueryOptions;
+use PHPUnit\Framework\TestCase;
+
+final class QueryOptionsTest extends TestCase
+{
+    public function test_constructor_sets_properties(): void
+    {
+        $createdBy = ['user-1', 'user-2'];
+        $subjectTypes = ['Expense'];
+        $subjectIds = ['exp-1', 'exp-2'];
+        $eventTypes = ['tracked'];
+
+        $options = new QueryOptions(
+            createdBy: $createdBy,
+            subjectTypes: $subjectTypes,
+            subjectIds: $subjectIds,
+            eventTypes: $eventTypes
+        );
+
+        self::assertSame($createdBy, $options->createdBy);
+        self::assertSame($subjectTypes, $options->subjectTypes);
+        self::assertSame($subjectIds, $options->subjectIds);
+        self::assertSame($eventTypes, $options->eventTypes);
+    }
+
+    public function test_is_empty_returns_true_for_empty(): void
+    {
+        $options = new QueryOptions();
+        self::assertTrue($options->isEmpty());
+    }
+
+    public function test_is_empty_returns_false_for_non_empty(): void
+    {
+        $options = new QueryOptions(createdBy: ['user-1']);
+        self::assertFalse($options->isEmpty());
+    }
+}